This invention relates in general to radiation shielding means, and more particularly to radiation shielding pellets containing at least two shielding materials within individual pellets.
Radiation shields often contain more than one type of material in order to provide attentuation over the entire spectrum of incident radiation. One common type of shielding application requires a gamma ray shielding metal such as tungsten or steel in combination with a hydrogen-rich neutron shielding material such as lithium hydride.
Since the radiation shield must provide uniform attenuation over a large surface area, the two required materials must be prevented from separating within the shield. This means that lithium hydride in a shield must be trapped in place. If it is allowed to liquify or form vapor bubbles, portions of the shield volume will come to have an incorrect ratio of LiH versus metal, and shielding will not be uniform.
Prior art shielding systems have dealt with this problem by attempting to maintain all portions of the shield below the melting point of LiH. The interior of the shield was filled with a honeycomb-like structure of tungsten or steel with LiH placed in the cells of the honeycomb. The metallic honeycomb conducted heat away from the LiH and to the outer surface of the shield.
However, honeycomb structures are difficult to fabricate, particularly if an active cooling means, such as a fluid flow heat removal system, is required. Moreover, honeycombs and cooling pipes required to maintain LiH in solid form tend to be heavy. This makes them undesirable for use in systems requiring active cooling which must be launched into space.
In addition, in shields wherein lithium hydride is cast and allowed to solidify, cracks often develop in the solid lithium hydride. These permit radiation to stream through.